The present invention relates to an ink follower for a writing tool and a writing tool at which the same is arranged. More particularly, for the purpose of the prevention of evaporation of water or an organic solvent in ink during storage or in use and the prevention of leaking or flow backward of ink in the writing tool where ink for writing is directly contained in an ink-containing reservoir, the invention relates to an ink follower for the writing tool which is charged in contact with the ink at the terminal part opposite to the part of the ink reservoir to which an writing tip is attached.
Hitherto, in a writing tool where ink for writing is directly contained in an ink-containing reservoir, e.g., a ballpoint pen, an ink follower is charged in contact with the ink at the terminal part of the ink reservoir for the purpose of the prevention of evaporation, leaking or flow backward of the ink. Such ink follower should be hardly volatile and have high apparent viscosity. For that purpose, ink followers where an organic or inorganic thickening agent, a gelling agent or the like is added to a base oil of a hardly volatile liquid or a nonvolatile liquid have been known.
For example, Japanese Patent Publication No. 64 -10554/1989 proposes a composition where an organic gelling agent such as dibenzylidene sorbitol is added to a hardly volatile solvent such as ethylene glycol, and Japanese Patent Application Laid-Open Publication No. 57-200472/1982 proposes a composition where an thickening agent such as an amino acid derivative is dissolved in polybutene or the like to form a gel.
In addition, those where an organic or inorganic thickening agent, a gelling agent or the like is added to a base oil of a hardly volatile liquid or a nonvolatile liquid and a specific additive is further added for the purpose of improving the performance are proposed in Japanese Patent Publication Nos. 5-82804/1993, 6-15277/1994, 6-33024/1994, 6-33025/1994, 6-33026/1994, 6-47318/1994, 7-17872/1995, 7-29513/1995, Japanese Patent No. 2677734, Japanese Patent Application Laid-Open Publication Nos. 4-202281/1992, 5-270193/1993, 6-200235/1994, 7-216285/1995, 8-11481/1996, 8-300874/1996, 9-234988/1997 and so forth.
In these gelling methods of the ink followers, gels are thickened by the network formation between the molecules of the gelling agents. In such system, since the gels are further thickened through the expansion of the networks between the molecules with the passage of time, there is a problem that the ink followers in which these gels are used become hard and difficult to follow ink. As a result, with the passage of time, insufficient following of the ink followers is observed in the ballpoint pens where such ink followers are arranged and there occur problems that writing lines become patchy and writing with the pen becomes impossible.
When the addition of the gelling agent is reduced in order to avoid these problems, the problem that the ink followers become hard with the passage of time is solved but impact resistance becomes insufficient and leaking and back leaking of the ink occur. Furthermore, oil separation, i.e., partial separation of the base oil occurs as time passed. Since the separated liquid is often lighter than ink, the separated liquid goes up through the ink and stays in the tip of a ballpoint pen to cause inconvenience in writing at the ballpoint pen which is left to stand with the tip upward.
In addition, Japanese Patent Application Laid-Open Publication No. 8-142570/1996 proposes an ink follower where a phthalate ester-type plasticizer and a polyester-type thermoplastic elastomer are combined. In the ink follower, it is attempted to cope with both the stability during the passage of time and the control of flow rate of ink but the ink follower is inferior in impact resistance, so that there is a problem that ink leaks out when external force is imposed by, for example, falling, vibration or the like.
In such situations, for enhancing impact resistance, the addition of non-swellable particles having a similar specific gravity to that of the base oil and a particle size of several tens to several hundreds xcexcm or the incorporation of rod-shaped materials of several mm is proposed in Japanese Patent Application Laid-Open Publication Nos. 10-44673/1998 and 10-67196/1998 but the problem of the oil separation is not yet solved.
As described above, there is no proposal of the ink follower having sufficient stability during the passage of time, impact resistance and ink-following ability as well as showing no oil separation.
An object of the present invention is to provide an ink follower for a writing tool having enhanced impact resistance without causing insufficient following and oil separation with the passage of time as well as with no inconvenience in writing, and to provide a writing tool at which the same is arranged. This invention relates to an ink follower for a writing tool comprising a swollen gel formed from an oil-absorbable resin and a base oil of a hardly volatile liquid and/or a nonvolatile liquid, wherein the ink follower is arranged in contact with the ink surface opposite to the part of an ink reservoir to which a writing tip is attached.
The present invention also relates to a writing tool wherein ink is directly charged into an ink reservoir and an ink follower is arranged in contact with the ink surface opposite to the part to which a writing tip is attached. The oil-absorbable resin may be a polymer having lipophilicity. The swollen gel which forms the ink follower may be a gel having a particle size of 30 to 2000 xcexcm. The swollen gel which forms the ink follower may be a mixture of a gel having a particle size of 30 to 100 xcexcm and a gel having a particle size of 300 to 1500 xcexcm. The amount of the oil-absorbable resin may be from 10 to 20% by weight of the ink follower. The oil-absorbable resin is one or more selected from acrylate ester crosslinked polymers and/or copolymers thereof, methacrylate ester crosslinked polymers and/or copolymers thereof, and polynorbornene.
Further, the writing tool may be the one that a writing tip is directly attached to an ink reservoir. Alternatively, the writing tool may be the other that a writing tip is attached to an ink reservoir through an ink-feed controller.